its the same in all programming.U define imports or libraries at the start of a code.such us #include <stdio.h> which stands for C or #include <iostream.h> for C++.Java u just import the "libraries"so you dont have to write the whole code again and again.Its like calling a code from somewhere as u do with desktop shortcuts.Example:
import net.sf.l2j.gameserver.instancemanager.RaidBossPointsManager;
import net.sf.l2j.gameserver.model.L2Skill;
import net.sf.l2j.gameserver.model.actor.L2Character;
import net.sf.l2j.gameserver.model.actor.L2Summon;
import net.sf.l2j.gameserver.network.SystemMessageId;
import net.sf.l2j.gameserver.model.actor.instance.L2PcInstance;
import net.sf.l2j.gameserver.network.serverpackets.Earthquake;
import net.sf.l2j.gameserver.network.serverpackets.ExRedSky;
import net.sf.l2j.gameserver.network.serverpackets.SystemMessage;
import net.sf.l2j.gameserver.templates.chars.L2NpcTemplate;
import net.sf.l2j.gameserver.util.Broadcast;
import net.sf.l2j.util.Rnd;
// RedSky and Earthquake and Announcement
ExRedSky packet = new ExRedSky(10);
Earthquake eq = new Earthquake(player.getX(), player.getY(), player.getZ(), 14, 3);
Broadcast.toAllOnlinePlayers(packet);
Broadcast.toAllOnlinePlayers(eq);
Broadcast.announceToOnlinePlayers(super.getName()+ " has been killed.");
This code doesnt work but just to give u to understand where the imports are.Always look at the start of every java.If u dont see the imports press the + which is included in a circle button to actualy access more code which is compressed inside that "+".If u still got problem getting the imports tell me what i said wrong